It's spring in the Gobi desert and the last pregnant camel of a nomadic Mongolian family's herd has given birth. The labour was traumatic for this rusty red camel and, unlike the other new mothers, her maternal instincts haven't kicked in.

Suffering the Bactrian (two-hump camel) equivalent of post-natal depression, the mother camel turns her back on her spindly white colt and trots off to the dunes to mope. The little camel is left wobbling across the sand after her, bleating uselessly for love and milk.

This is the striking conflict in the The Weeping Camel, a film that's part nature doco, part anthropological study and part drama, with the animals taking the starring roles. Italian co-director Luigi Falorni says the hardest part was finding a camel that would reject her young for the film.

"We travelled for about 4000 kilometres around the desert to find the right family," says 33-year-old Falorni, who worked on the film with Mongolian-born director Byambasuren Davaa. The pair met studying at the Munich Academy of Television and Film in the late '90s.

The idea was Davaa's. She wanted to film a ritual she had seen in an educational documentary as a child in Mongolia. Every now and then, a mother camel rejects her young, so the Gobi dwellers perform a musical ritual that softens the heart of the mother and coaxes her to bond with her calf.

The filmmakers gave themselves less than two months to shoot the documentary. They chose to film the family with the greatest number of pregnant camels, gambling that one of the mothers would reject her calf.

Over six weeks, 19 camels delivered. When 19 mother-and-calf pairs were happy, the filmmakers were despondent.

"We didn't have a B plan, so if the rejection didn't happen, no film, or maybe just wait around for something else to happen," Falorni says.

The co-directors were wondering how they would explain to the German TV network and film funding bodies what they had done with their money when serendipity struck.

"We had been to a delivery the night before that went well," Falorni says. "The very last camel was left, and we spent the next night waiting for it to happen, as camels usually give birth at night. I slept with my camera on my arm ready to shoot and one of us kept watch.

Uuganbaatar Ikhbayar as Ugna

"As day broke, the crew of 11 were told by the family to go back to our tents and go to sleep. We drove to our camp half a kilometre away from their camp, and as we were starting to relax our walkie-talkie went off. The delivery was happening."

Luckily for the filmmakers, not only was the last camel born a rare white colt, but the mother abandoned it.

The filmmakers concentrated on filming the musical ritual that reunites the camel mother with the calf.

The nomad family pull the two camels together, and a Mongolian musician, playing a Mongolian violin, plays music while one of the family sings the sound "hoos" repeatedly.

Falorni says that the nomadic Mongolians use a different sound for different species - for a sheep that has rejected her lamb it's "toig".

Watching the ritual on screen is eerie. How can singing "hoos" reconcile a mother to its child after she has denied him milk, kicked him away from her and left him for dead?

Falorni says no one knows how it works.

"It hasn't really been studied, as far as I know," he says. "There are animal farms that do play music to soothe the animals.

"There's a study that showed plants grow better with classical music and shrink to rock music."

Incredibly, the film also shows the mother camel weeping as she listens to the music. Falorni denies the filmmakers stuck an onion under the camel's eye to induce tears.

"I didn't believe it, either, but it's what usually happens in this situation," Falorni says.

"That's what gave me some confirmation about this. We saw the short educational film about the ritual shot in Mongolia and the camel cries in that, too. The nomads say the ritual always works."

In the end, it's the animals that transfix.

The little camel's cries are gut-wrenching and the mother kicking the calf away is painful to watch.

"The little camel would have died unless the mother reconciled with it," Falorni says.

"A camel needs two years of mothering. There is one scene with the camels alone and the mother was running away from him. That was when tears were in our eyes. We just had to keep the camera rolling."